Electrode of selenides or tellurides

ABSTRACT

A fuel electrode whose catalytic component is chosen from the group consisting of the tellurides and selenides of the elements molybdenum, tungsten, and chromium.

United States Patent Pohl et al.

[451 Sept. 23, 1975 ELECTRODE OF SELENIDES OR TELLURIDES Inventors:Franz Arthur Pohl, Gotzenhain;

Harald Biihm, Oberursel, both of Germany Assignee: LicentiaPatent-Verwaltungs G.m.b.H., Frankfurt, Germany Filed: June 9, 1970Appl. No.: 44,797

Foreign Application Priority Data June 9, 1967 Germany 19291161 U.S. Cl.136/121; 136/86 D; 136/120 EC Int. Cl. HOlm 13/02 Field of Search136/120 R, 120 PC, 121,

References Cited UNITED STATES PATENTS 3,031,518 4/1962 Werner et a1136/86 A 3,223,556 12/1965 Cohn et al. 136/86 3,324,025 6/1967 Hackerman136/86 D 3,380,856 4/1968 Pohl 136/120 FC 3,471,412 10/1969 Miale et a1252/439 Primary Examinerl Dewayne Rutledge Assistant Examiner M. .1.Andrews' Attorney, Agent, or Firm-Spencer & Kaye [57] ABSTRACT A fuelelectrode whose catalytic component is chosen from the group consistingof the tellurides and selenides of the elements molybdenum, tungsten,and chromium.

3 Claims, 1 Drawing Figure US Patent Sept. 23,1975 3,907,600

INVENTORS. Franz Arrher Pohl Harald B6hm BY 52;, Z)

ATTORNEYS.

ELECTRODE OF SELENIDES OR TELLURIDES BACKGROUND OF THE INVENTION Thepresent invention relates to a fuel electrode for a fuel cell.

It is known to use electrocatalysts such as nickel and platinum for theelectrochemical burning of fuels in fuel cells. The disadvantages ofsuch known catalysts lie either in their being too valuable forcommercial use, as in the case of platinum, or in their being poisonedby the fuel or by impurities contained in the fuel, whereby catalyticabilities are lost.

It has also already been proposed to use an electrode of tungstencarbide for the electrochemical oxidation of impure hydrogen usingimpure atmospheric oxygen.

SUMMARY OF THE INVENTION An object of the present invention, therefore,is to provide a fuel electrode that not only gives a continued burningof impure, gaseous fuels, but in addition makes possible anelectrochemical burning of dissolved fuels at high efficiency.

This as well as other objects which will become apparent in thediscussion that follows are achieved, according to the presentinvention, by providing a fuel electrode containing one or moretellurides and/or selenides of the elements molybdenum, tungsten, orchromium.

In a further development of the present invention, the catalyticactivity of the electrodes of the present invention is improved by theaddition of a molybdenum and/or tungsten sulfide.

Surprisingly, it has been found that an electrocatalysts according tothe invention can be used for the electrochemical conversion of gaseousfuels composed essentially of carbon monoxide, without experiencingdegeneration of catalytic abilities. Thus, for example, gas obtained byreforming natural gas or liquid hydrocarbons can be oxidized in aconventional fuel cell using the catalysts of the present invention.Quite surprisingly such gases can be converted at high current densityin a low temperature fuel cell, ie one operating at below 100C.

Should the fuels contain hydrogen sulfide, elemental sulfur is a usefulby-product obtained using the electrodes according to the presentinvention.-

According to a preferred further development of the present invention,the electrode of the present invention is used for the electrochemicalconversion of dissolved fuels such as alchohols, aldehydes, andcarboxylic acids. It has been surprisingly found that the oxidation offormaldehyde or formic acid proceeds with an efficiency never beforeachieved.

BRIEF DESCRIPTION OF THE DRAWINGS The sole FIGURE of the drawing is apartly schematic, elevational, cross-sectional view of a half-cell usedfor evaluating the electrode of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The tellurides. selenides, andsulfides of the present invention have relatively small electricalconductivi ties, so it is preferred to mix them with additives havinghigher electrical conductivities when forming them into electrodes.Especially favorable for such purposes is hard coal or tungsten carbidein amounts of ten to 50 volume percent. Depending on whether theelectrodes of the present invention are used for the electrochemicalburning of gaseous or of dissolved fuels, they are either provided asgas-diffusion or as immersion electrodes.

The electrodes of the present invention are prepared by firstpulverizing the raw materials and then mixing them with a thermoplasticmaterial. The mixture is then pressed and finally sintered. Sinceimmersion electrodes generally must have less porosity than gasdiffusion electrodes and moreover must possess hydrophilic properties,it is preferred to use less plastic for their production. Suitablethermoplastic materials are polyethylene, polyp'ropylene, polycarbonate,and halogenated polyolefins.

Further illustrative of the present invention are the followingexamples:

EXAM PLE I The following powders are mixed:

50 volume-7: MoSe powder having a particle size of less than 1 micron;

30 volume-71 conductive, porous hard coal having a particle size of 10microns as supplied by Ringsdorffwerke, D-532 Bad Godesberg-Mehlem,Germany, under the name EK l5" and 20 volume-7z polyethylene ofparticles size range between and I50 microns.

The above-mentioned hard coal has a resistivity of 6 X 10ohm.centimeters and an ash content of 1.0 weight-'/z. This material ischosen as additive because its particles are porous, it is stableagainst corrosion, and has good electrical conductivity.

The mixture is compacted at a pressure of 0.55 X 10" ponds per cm into adisc-shaped fuel electrode having a thickness of 2 millimeters and adiameter of 34 millimeters.

This electrode is sintered at C for 3 0 minutes.

The thus made electrode is evaluated in the half-cell arrangementillustrated in the FIGURE of the drawing. Glass vessel 1 containsZ-normal sulfuric acid as electrolyte, which is indicated by water level2. The electrode a in the form ofa disc as above prepared is sealed inthe immersed end of a transparent, non-conductive, plastic tube 3 made,for instance, of Arylglas. Hydrogen reference electrode b is constructedaccording to J. Giner, A Practical Reference Electrode, J. Electrm chem.800., Volume Ill (1964), page 376. A carbon rod 0 serves ascounter-electrode. Such apparatus is described in Wolframcarbid, einElektrokatalysator fur saure Brennstoffzellen by Harald Bohm and FranzA. Pohl, WissenschafiIic/re Berk-lite AEG-Telefimkem Vol. 4] 1968),pages 4649, while similar apparatus is described in Brennstoffelements"by Wolf Vielstich, Verlag Chemie I965, pages 27-30.

Evaluation is carried out at an electrolyte temperature of 60C. Carbonmonoxide is caused to flow as fuel down tube 3, through disc :1, at apressure of I50 millimeters of water and a flow rate of around 2-5liters/ hr as measured at 25C and one atmosphere pressure. When there isno current flowing between the electrode disc 0 of this example and thecounter-electrode c, a relatively low voltage of 30 millivolts ismeasured between the hydrogen reference electrode 12 and the electrodedisc u. When a current is introduced at terminals 4 and 5 to flowbetween counter-electrode and electrode disc u with electron flow beingfrom electrode c, through the electrolyte. to electrode a to pro duce acurrent density on electrode a of 9 milliamperes per cm a referencevoltage U of 200 millivolts is measured across terminals 5 and 6. Oncethis current density is obtained at a certain voltage drop acrossterminals 4 and 5, it remains constant as time of operation increases.

EXAMPLE ll One proceeds as in Example 1, except that instead of 50volume- /z MoSe the mixture contains 25 volume-71 tungsten disulfide (W5having a particle size of less than 1 micron; and 25 volume- /l tungstentelluride (WTehaving a particle size of less than 1 micron. Formaldehydeis used as fuel, dissolved in the electrolyte at a 2-molarconcentration, instead of the carbon monoxide of Example I. Theresulting immersion electrode provides, under the experimentalconditions set forth in Example I, at zero-current U of millivolts. Witha current density of 12 milliamps per cm U 200 millivolts, electron flowbeing in the direction of Example I. Also in this example, no fall incurrent density is experienced with time. Tube 3 functions in thisexample only as a supporting means for the electrode (1.

EXAMPLE lll One proceeds as in Example 1, except that instead of 50volume-% MoSe. the mixture contains 50 volume- /r tungsten diselenide(WSe having a particle size of less than 1 micron.

Using hydrogen as fuel at a pressure of 150 millimeters H. ,O, flow rateof 25 liters per hour, instead of the carbon monoxide of Example I, theresulting electrode 0 provides. under the experimental conditions setforth in Example I, voltage U of 200 millivolts at 38 milliamps per cmcurrent density.

EXAMPLE 1V One proceeds as in Example I, except that instead of 50volume- /r M()Se2, the mixture contains volume-71 molybdenum disulfide(MOS-1) having a particle size of less than 1 micron; and

25 volume-7r tungsten diselenide (WSe having a particle size of lessthan 1 micron.

Using as fuel, instead of the carbon monoxide of Example l, a gasmixture containing 50 volume-% hydrogen, 25 volume-7t carbon monoxide.and 25 volume-7r hydrogen sulfide, at a pressure of l50 millimeters ofwater, this gas-diffusion electrode provides, under the experimentalconditions set forth in Example I, a voltage U of 200 millivolts at acurrent density of 42 milliamperes per cm. Also in this example, no fallin current density is experienced with time.

EXAMPLE V An electrode is prepared as in Example 1, except that insteadof the volume-% hard coal, the mixture contains 30 volume-i2 tungstencarbide (WC) having a particle size of 2.5 microns.

EXAMPLE Vl Tungsten carbide (WC) of 2.5 micron particle size issuspended in water and sufficient ammonium selenotungstate is added toprovide a tungsten carbide to tungsten diselenide (WSevolume ratio of30/50 in the final product. Then o-normal hydrochloric acid is addeduntil the moles of hydrochloric acid in the solution equal the moles ofammonuim ion. This causes tungsten triselenide to precipitate on thesuspended tungsten carbide particles. The mixture is then filtered anddried. Upon heating at 350 to 450C, the tungsten triselenide on thetungsten carbide is converted to tungsten diselenide.

One then proceeds to mix in the 20 volume-% polyethylene of Example I.Further details in the preparation of an electrode are the same as inExample 1.

EXAMPLE Vll One proceeds as in Example Vl, except that instead of theammonium selenotungstate, ammonium selenomolybdate is used.

EXAMPLE viii One proceeds as in Example ll, except that instead offormaldehyde as fuel, CH OH is used, dissolved in the electrolyte at a2molar concentration. At U 400 millivolts, the current density is 0.8milliamps per cm.

EXAMPLE lX One proceeds as in Example ll, except that instead offormaldehyde as fuel. formic acid is used, dissolved in the electrolyteat 2-molar concentration. At U 200 millivolts, the current density is 6milliamps per cm".

Electrochemical burning of fuels in no case led to an impairment of theactivity of the electrode catalysts of the present invention.

Electrodes may be made of the tellurides of molybdenurn and tungsten.chromium selenide, and chromium tellurideanalogously to the processgiven in Example I for MoSe It will be understood that the abovedescription of the present invention is susceptible to variousmodifications, changes and adaptations, and the same are intended to becomprehended within the meaning and range of equivalents of the appendedclaims.

We claim:

1. An electrode consisting essentially of at least one compound selectedfrom the group consisting of the tellurides and selenides of theelements molybdenum,

tungsten and chromium, and further containing at least one compoundselected from the group consisting of molybdenum sulfide and tungstensulfide.

2. An electrode as claimed in claim 1, further containing means forincreasing effective electrical conductivity.

3. An electrode as claimed in claim 2, said means being selected fromthe group consisting of hard coal and tungsten carbide.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 2 3,907,600

DA E I September 23, 1975 INVENTOR( I Franz Arthur Pohl et al It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In the heading of the patent, under [30] Foreign Application PriorityData, change "1967" to -l969- and change "19291161" to 1929161.

Column 3, line 22, after "current" insert an-.

Signed and Sealed this second Day of March 1976 [SEAL] Arrest:

RUTH C. MA.SON C. MARSHALL DANN A! I 951mg ff (omrm'ssimwr uj'Parenrsand Trademarks

1. AN ELECTRODE CONSISTING ESSENTIALLY OF AT LEAST ONE COMPOUND SELECTEDFROM THE GROUP CONSISTING OF THE TELLURIDES AND SENIDES OF THE ELEMENTSMOLYBDENUM, TUNGSEN AND CHROMIUM, AND FUTHER CONTAINING AT LEAST ONECOMPOUND SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM SULFIDE ANDTUNGSTEN SULFIDE
 2. An electrode as claimed in claim 1, furthercontaining means for increasing effective electrical conductivity.
 3. Anelectrode as claimed in claim 2, said means being selected from thegroup consisting of hard coal and tungsten carbide.